How to fill NAs with LOCF by factors in data frame, split by country

Question

I have the following data frame (simplified) with the country variable as a factor and the value variable has missing values:

country value
AUT     NA
AUT            


        

Answer 1

You simply need to split by country, then a do either a zoo::na.locf() or na.fill, filling to the right. Here is an example explicitly showing the three-component arg syntax of na.fill:

library(plyr)
library(zoo)

data <- data.frame(country=c("AUT", "AUT", "AUT", "AUT", "GER", "GER", "GER", "GER", "GER"), value=c(NA, 5, NA, NA, NA, NA, 7, NA, NA))

# The following is equivalent to na.locf
na.fill.right <- function(...) { na.fill(..., list(left=NA,interior=NA,right="extend")) }

ddply(data, .(country), na.fill.right)

  country value
1     AUT  
2     AUT     5
3     AUT     5
4     AUT     5
5     GER  
6     GER  
7     GER     7
8     GER     7
9     GER     7